The present invention relates to video signal aspect conversion for converting the aspect ratio of a video picture and, more particularly, to converting the aspect ratio in accordance with an identification signal added to the video picture.
A video picture has an aspect ratio, which is the ratio of the width to the height of the picture. The aspect ratio varies according to different video picture systems. Television receivers employing the NTSC System, for example, produce a video picture with an aspect ratio of 4:3. Thus, the display screen is substantially square, the width being only 1.34 times greater than the height.
By comparison, a typical movie picture has an aspect ratio of 16:9, which is rectangular and has a significantly greater width to height ratio than the NTSC system. This movie picture is known as a wide screen picture and is much more optically pleasing than the substantially square 4:3 video picture because people normally perceive their surroundings with a greater sense of width than height.
Recently, televisions having a wide display screen, i.e., 16:9, aspect ratio have been produced so that people can watch video recorded movies in the comfort of their own home with all the enjoyment of watching the movie in a movie theater. These wide-screen televisions receive wide-screen video signals, just as the NTSC system televisions receive so-called 4:3 video signals.
A problem arises, however, when a NTSC 4:3 television receives a wide-screen 16:9 video signal because the number of horizontal lines of a wide-screen video signal does not correspond to the number of horizontal lines of the NTSC television. A wide-screen video signal has 360 horizontal lines, whereas the NTSC video signal has 525 horizontal lines. As a result, if a wide-screen video picture is displayed on a NTSC television, upper and lower portions of the video picture, as shown in FIG. 16c, are blank. This configuration is visually unappealing because it appears "squashed" to an observer and the left and right portions of the wide-screen picture are cut off. This is a particular problem when the cut-off portions include important picture information; and as a result, the viewer does not perceive an important part of the video picture.
Similarly, if a 4:3 video picture is displayed on a 16:9 wide-screen television, left and right portions of the video picture are blank. This is because the 4:3 video picture has a smaller width than the width of the wide-screen television. Similar to the case of the wide-screen video picture displayed on an NTSC television, the top and bottom portions of the original picture are cut off in the 4:3 television as shown in FIG. 17d.
Another problem associated with displaying a 16:9 wide-screen video signal on a 4:3 television is that the vertical resolution of the displayed picture is reduced. This is because the number of effective scanning lines in the vertical direction for a wide-screen video signal is 360 and the number of scanning lines for a 4:3 television is 525. Even if the number of scanning lines of the wide-screen video signal is increased to about 480 by means of an interpolation process, it still is not possible to obtain the same vertical resolution of the original picture. This is because the wide-screen video signal would be produced by decimating a video signal of 480 lines to 360 lines and some of the vertical resolution is lost in the process.
A technique proposed to fit a wide-screen video signal on a 4:3 television is shown by FIGS. 18a-d. The original picture shown in FIG. 18a is vertically stretched into the NTSC video picture shown in FIG. 18b. However, the resulting vertically stretched picture appears abnormal to an observer and is, therefore, not desirable.